The apparatus according to an aspect of the present invention includes a roll conveyor having vertically movable rolls, the roll conveyor thereby being adjustable for arching the conveyor to a curvature matching a desired degree of bending around a bending axis which is transverse to the advancing direction of glass sheets or parallel to the rolls. The apparatus further includes lower tempering boxes having top surfaces provided with tempering orifices, and upper tempering boxes having bottom surfaces provided with tempering orifices. The tempering boxes are movable for moving the top and bottom surfaces to comply with the arching of the conveyor. This type of apparatus is prior known from the Applicant's Patent publications U.S. Pat. No. 4,881,962 and U.S. Pat. No. 5,057,137. This apparatus has proved highly useful in the production of bent and tempered construction glass.
In this prior known apparatus, the bending of a glass sheet is based on gravitational deflection within a bending and tempering station outside a heating furnace. For this reason it is sometimes necessary to overheat the glass relative to a required tempering temperature as the glass temperature falls before the glass has completely bent to its desired configuration and the glass tempering can be commenced.
Depending on the glass types and conditions, the cooling of glass is typically in the order of 10.degree. C.-25.degree. C.
A characterizing feature for this so-called overheating in that the optical errors of glass are accentuated and are more perceivable in the end product.
In addition, a limitation in this prior known method and apparatus is that a glass sheet can only be bent or deflected relative to a single axis of curvature.
An object of the invention is to improve the above known method and apparatus such that glass can be bent to produce a double curvature and, in addition, harmful overheating can be eliminated from the process for reducing the temperature of glass coming out of a furnace and for improving the glass optics.
When adjustable press rollers are included above the glass, the gravitational bending is converted into mechanical press bending. When the glass is also supported on the rolls of an arched roll conveyor, with the mid-section of the rolls at a lower level than the ends of the rolls, the bending will be achieved around two axes perpendicular to each other and, in addition, the glass sheet will have a bent shape with improved precision as the bending can be controlled and forced to a desired shape.
The bending of glass with a set of upper and lower rollers in a combined bending and tempering station has already been proposed in the Patent publication U.S. Pat. No. 4,822,398. According to that patent, however, the bending is solely effected around a bending axis parallel to the advancing direction of a glass sheet. A double curvature cannot be achieved and, in addition, the rather small radii of curvature causes optical problems due to the fact that the rolls responsive to either surface of the glass during the course of bending shift laterally relative to the glass, i.e. slide along the glass surface in the direction transverse to the advancing direction. This makes it difficult to fulfill requirements for high optical quality. In the present invention, the bending with a smaller radius of curvature can be selected around an axis transverse to the advancing direction. The flexible suspension of press rolls and the press force adjustable during the course of bending enable the adaptation of the invention to benders in which the bending is effected around axes both transverse and parallel to the advancing direction.